U.S. patent application number 12/096981 was filed with the patent office on 2009-08-13 for method of manufacturing fuel cell.
Invention is credited to Satoshi Aoyama.
Application Number | 20090200172 12/096981 |
Document ID | / |
Family ID | 37757122 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090200172 |
Kind Code |
A1 |
Aoyama; Satoshi |
August 13, 2009 |
METHOD OF MANUFACTURING FUEL CELL
Abstract
A method of manufacturing a fuel cell includes thermally
treating a hydrogen permeable membrane in a given temperature
higher than an actual operating temperature of the fuel cell, and
forming an electrolyte layer on the hydrogen permeable membrane
subjected to the thermal treatment. The hydrogen permeable membrane
is composed of a polycrystalline metal.
Inventors: |
Aoyama; Satoshi;
(Shizuoka-ken, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
37757122 |
Appl. No.: |
12/096981 |
Filed: |
December 6, 2006 |
PCT Filed: |
December 6, 2006 |
PCT NO: |
PCT/JP2006/324783 |
371 Date: |
June 11, 2008 |
Current U.S.
Class: |
205/88 ;
205/209 |
Current CPC
Class: |
Y02E 60/525 20130101;
H01M 4/8885 20130101; C01B 2203/066 20130101; B01D 53/228 20130101;
B01D 67/0083 20130101; H01M 8/124 20130101; H01M 2004/8684
20130101; H01M 4/94 20130101; H01M 4/9058 20130101; Y02P 70/56
20151101; B01D 71/022 20130101; Y02E 60/50 20130101; B01D 2323/08
20130101; H01M 2300/0068 20130101; C01B 3/505 20130101; H01M 8/126
20130101; Y02P 70/50 20151101 |
Class at
Publication: |
205/88 ;
205/209 |
International
Class: |
H01M 8/12 20060101
H01M008/12; C25D 7/00 20060101 C25D007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2005 |
JP |
2005-359741 |
Claims
1. A method of manufacturing a fuel cell comprising: thermally
treating a hydrogen permeable membrane in a hydrogen atmosphere at
a given temperature higher than an actual operating temperature of
the fuel cell for a given time; and forming an electrolyte layer on
the hydrogen permeable membrane subjected to the thermal treatment,
wherein: the hydrogen permeable membrane is composed of a
polycrystalline metal; and the given time is a time so that a
diffusion length calculated with the given time, the given
temperature and a diffusion coefficient of the hydrogen permeable
membrane is more than a diffusion length calculated with the
diffusion coefficient, the actual operating temperature and an
actual operating time of the fuel cell.
2. A method of manufacturing a fuel cell comprising: thermally
treating a hydrogen permeable membrane in a hydrogen atmosphere,
the hydrogen permeable membrane being a polycrystalline metal
composed of palladium or palladium alloy; and forming an
electrolyte layer on the hydrogen permeable membrane subjected to
the thermal treatment.
3. The method as claimed in claim 2, wherein the hydrogen permeable
membrane is subjected to the thermal treatment at a temperature
higher than 200 degrees C.
4. The method as claimed in claim 2, wherein the hydrogen permeable
membrane is subjected to the thermal treatment at a temperature
higher than 600 degrees C.
5. The method as claimed in claim 2, wherein the hydrogen permeable
membrane is subjected to the thermal treatment for a given
time.
6. The method as claimed in claim 5, wherein the given time is a
time so that a diffusion length calculated with the given time, a
thermal treatment temperature and a diffusion coefficient of
palladium in the hydrogen permeable membrane is more than a
diffusion length calculated with the diffusion coefficient, an
actual operating temperature and an actual operating time of the
fuel cell.
7. The method as claimed in claim 2, wherein the electrolyte layer
is composed of a perovskite electrolyte or a solid acid
electrolyte.
Description
TECHNICAL FIELD
[0001] This invention generally relates to a method of
manufacturing a fuel cell.
BACKGROUND ART
[0002] One or more aspects of this invention generally relate to a
method of manufacturing a fuel cell.
[0003] In general, a fuel cell is a device that obtains electrical
power from fuel, hydrogen and oxygen. Fuel cells are being widely
developed as an energy supply system because fuel cells are
environmentally superior and can achieve high energy
efficiency.
[0004] There are some types of fuel cells including a solid
electrolyte such as a polymer electrolyte fuel cell, a solid-oxide
fuel cell, and a hydrogen permeable membrane fuel cell (HMFC).
Here, the hydrogen permeable membrane fuel cell has a dense
hydrogen permeable membrane. The dense hydrogen permeable membrane
is composed of a metal having hydrogen permeability, and acts as an
anode. The hydrogen permeable membrane fuel cell has a structure in
which a solid electrolyte having proton conductivity is deposited
on the hydrogen permeable membrane. Some hydrogen provided to the
hydrogen permeable membrane is converted into protons. The protons
are conducted in the electrolyte having proton conductivity and
react with oxygen provided to a cathode. Electrical power is thus
generated.
[0005] Japanese Patent Application Publication No. 2004-146337, for
example, proposes a method of forming a
proton-conductive-electrolyte layer on a substrate of dense metal
having hydrogen permeability. According to the method, it is
possible to reduce the thickness of the electrolyte layer.
[0006] However, it is possible that a boundary separation between
the electrolyte layer and the substrate occurs because of an uneven
surface of the substrate.
[0007] Various aspects of this invention have been made in view of
the above-mentioned circumstances. One or more aspects of the
invention provide a method of manufacturing a fuel cell in which a
boundary separation between a solid electrolyte layer having proton
conductivity and a metal substrate having hydrogen permeability is
limited.
DISCLOSURE OF THE INVENTION
[0008] In exemplary embodiments, a method of manufacturing a fuel
cell includes thermally treating a hydrogen permeable membrane in a
given temperature higher than an actual operating temperature of
the fuel cell, and forming an electrolyte layer on the hydrogen
permeable membrane subjected to the thermal treatment. The hydrogen
permeable membrane is composed of a polycrystalline metal. In the
method, the hydrogen permeable membrane of the crystalline metal is
subjected to the thermal treatment in the given temperature higher
than the actual operating temperature. After that, the electrolyte
layer is formed on the hydrogen permeable membrane. In this case,
the metal included in the hydrogen permeable membrane diffuses
sufficiently. And a crystal grain is deformed sufficiently. It is
therefore possible to restrain the deformation of the hydrogen
permeable membrane after the thermal treatment. Accordingly, it is
possible to restrain the boundary separation between the hydrogen
permeable membrane and the electrolyte layer caused by the
deformation of the hydrogen permeable membrane.
[0009] In the exemplary embodiment, the hydrogen permeable membrane
may be subjected to the thermal treatment for a given time. And the
given time may be a time so that a diffusion length calculated with
the given time, the given temperature and a diffusion coefficient
of the hydrogen permeable membrane is more than a diffusion length
calculated with the diffusion coefficient, the actual operating
temperature and an actual operating time of the fuel cell. In this
case, the metal diffuses sufficiently so that each of the crystal
grains is no more sintered or recrystallized. It is therefore
possible to restrain the deformation of the hydrogen permeable
membrane after the thermal treatment.
[0010] An atmosphere may be a vacuum in the step of thermally
treating the hydrogen permeable membrane. In this case, it is
possible to facilitate the metal diffusion in the hydrogen
permeable membrane. And an atmosphere may be a hydrogen atmosphere
in the step of thermally treating the hydrogen permeable membrane.
In this case, it is possible to facilitate the metal diffusion in
the hydrogen permeable membrane.
[0011] In the exemplary embodiment, the hydrogen permeable membrane
may be subjected to the thermal treatment in a temperature higher
than the actual operating temperature of the fuel cell by more than
200 degrees centigrade.
EFFECT OF THE INVENTION
[0012] In accordance with the invention, a boundary separation
between a hydrogen permeable membrane and an electrolyte layer
caused by a deformation of the hydrogen permeable membrane is
restrained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Exemplary embodiments of one or more aspects of the
invention will be described with reference to the following
drawings, wherein:
[0014] FIG. 1A through FIG. 1E illustrate a schematic view of a
method of manufacturing a fuel cell in accordance with an
embodiment;
[0015] FIG. 2A through FIG. 2C illustrate aspects of a surface of
samples 1-1 and 1-2 after a thermal treatment;
[0016] FIG. 3A through FIG. 3D illustrate aspects of a surface of
samples 2-1 through 2-3 after a thermal treatment; and
[0017] FIG. 4A through FIG. 4C illustrate a surface profile of each
sample after a thermal treatment.
BEST MODE FOR CARRYING OUT THE INVENTION
[0018] FIG. 1A through FIG. 1E illustrate a schematic view of a
method of manufacturing a fuel cell 100 in accordance with an
embodiment. As shown in FIG. 1A, a hydrogen permeable membrane 10
having a thickness of approximately 20 .mu.m is provided. The
hydrogen permeable membrane 10 in accordance with the embodiment is
composed of a polycrystalline metal that is formed by rolling and
has hydrogen permeability. Palladium, vanadium, tantalum,
zirconium, niobium, an alloy thereof or the like may be used as the
polycrystalline metal having hydrogen permeability. In the
embodiment, the hydrogen permeable membrane 10 is a thin layer
composed of a plurality of palladium crystal grain. The grain is
referred to a crystal grain 11. An average diameter of the crystal
grains 11 is approximately a few .mu.m to a few tens of .mu.m.
[0019] Next, as shown in FIG. 1B, the hydrogen permeable membrane
10 is subjected to a thermal treatment. In this case, each of the
crystal grains 11 is deformed so that grain boundary free energy
and surface free energy are reduced, because a metal included in
the crystal grain 11 diffuses. Thus, as shown in FIG. 1C, the
surface of the crystal grain 11 is smoothed. And a grain boundary
groove 12 is formed between each of the crystal grains 11. It is
preferable that the hydrogen permeable membrane 10 is subjected to
the thermal treatment until each of the crystal grains 11 is no
more sintered or recrystallized, because it is restrained that the
crystal grain 11 is deformed by another thermal treatment after
that.
[0020] Next, as shown in FIG. 1D, an electrolyte layer 20 having
proton conductivity is formed on the hydrogen permeable membrane
10. In this case, the electrolyte layer 20 fills the grain boundary
groove 12 and covers the hydrogen permeable membrane 10. The
electrolyte layer 20 may be composed of a
proton-conductivity-material such as a perovskite
proton-conductivity-material (BaCeO.sub.3 or the like) or a solid
acid proton-conductivity-material (CsHSO.sub.4 or the like). The
thickness of the electrolyte layer 20 may be approximately 1 .mu.m.
Next, as shown in FIG. 1E, a cathode 30 is formed on the
electrolyte layer 20. The fuel cell 100 is fabricated through the
operations mentioned-above.
[0021] In the method of manufacturing the fuel cell in accordance
with the embodiment, the hydrogen permeable membrane 10 is
subjected to the thermal treatment in advance, and each of the
crystal grains 11 is deformed sufficiently. It is therefore
possible to restrain the boundary separation between the hydrogen
permeable membrane 10 and the electrolyte layer 20 caused by the
deformation of the crystal grain 11, even if the hydrogen permeable
membrane 10 is heated by the power generation reaction or even if
the hydrogen permeable membrane 10 is heated when the electrolyte
layer 20 is formed. A description will be given of details of
thermal treatment temperature, thermal treatment time, and thermal
treatment atmosphere.
[0022] In general, an average diffusion length X.sub.m of a metal
atom included in a solid metal is shown as following Expression
1.
X.sub.m=2(Dt/.pi.).sup.0.5 (Expression 1)
[0023] "t" in Expression 1 is time. "D" in Expression 1 is a
diffusion coefficient and is shown as following Expression 2.
D=D.sub.0exp(-Q/RT) (Expression 2)
[0024] "R" in Expression 2 is a gas constant. "T" in Expression 2
is an absolute temperature. In a case where palladium is used, "Q"
is 256 kJ and "D.sub.0" is 0.0000205 m.sup.2/s. As shown in
Expressions 1 and 2, the average diffusion length X.sub.m is
increased when the temperature T gets higher.
[0025] It is possible to calculate an average diffusion length
X.sub.Pd of palladium included in the hydrogen permeable membrane
10 during the operation of the fuel cell 100, if an actual
operating time of the fuel cell 100 is assigned to "t" in
Expression 1 and an actual operating temperature of the fuel cell
100 is assigned to "T" in Expression 2. Here, the actual operating
temperature is the operating temperature of the fuel cell 100 and
is, for example, approximately 200 degrees centigrade to 600
degrees centigrade. The actual operating time is an operating time
of the fuel cell 100 supposed in advance and is, for example,
approximately 5,000 hours to 100.000 hours. The palladium in the
hydrogen permeable membrane 10 diffuses sufficiently so that each
of the crystal grains 11 is no more sintered or recrystallized, if
the fuel cell 100 is operated for the actual operating time.
[0026] On the other hand, it is possible to diffuse the palladium
in the hydrogen permeable membrane 10, if the hydrogen permeable
membrane 10 is subjected to the thermal treatment. In this case, it
is possible to reduce the time of the thermal treatment to a large
degree, if the thermal treatment temperature is set to be higher
than the actual operating temperature. Examples are shown in Table
1. As shown in Table 1, it is possible to reduce the thermal
treatment time to approximately 1 or 2 hours, if the thermal
treatment temperature is increased to a temperature higher than the
actual operating temperature by approximately 200 degrees
centigrade. It is therefore possible to diffuse the palladium in
the hydrogen permeable membrane 10 advantageously.
TABLE-US-00001 TABLE 1 (Actual operating temperature) .times.
(Thermal treatment temperature) .times. (Actual operating time)
(Thermal treatment time) (400 degrees C.) .times. (50,000 hours)
(600 degrees C.) .times. (1 hour) (450 degrees C.) .times. (50,000
hours) (700 degrees C.) .times. (0.6 hours) (500 degrees C.)
.times. (50,000 hours) (750 degrees C.) .times. (2 hours)
[0027] It is thus possible to restrain the deformation of the
crystal grain 11 if the hydrogen permeable membrane 10 is subjected
to the thermal treatment sufficiently in advance. It is therefore
preferable that the thermal treatment time and the thermal
treatment temperature are set so that the diffusion length of the
palladium in the hydrogen permeable membrane 10 is more than a
diffusion length in a case where the fuel cell 100 is operated at
the actual operating temperature for the actual operating time. It
is more preferable that the thermal treatment temperature is higher
than the actual operating temperature from a viewpoint of reduction
of cost, because the thermal treatment time is reduced to a large
degree.
[0028] An atmosphere in the case of the thermal treatment is not
limited. It is preferable that the atmosphere is vacuum of few tens
of Pa or an inert gas atmosphere such as noble gas or nitrogen. The
atmosphere is preferably hydrogen, because metal diffusion is
facilitated by hydrogen diffusion. It is therefore possible to
reduce the thermal treatment time. Accordingly, it is possible to
reduce the production cost of the fuel cell 100.
[0029] In a case where other hydrogen permeable polycrystalline
metal except for palladium is used as the hydrogen permeable
membrane 10, it is possible to obtain the advantage of the present
invention if the thermal treatment temperature is set to be higher
than the actual operating temperature and lower than a melting
temperature of the hydrogen permeable membrane 10. Other hydrogen
permeable membrane formed through any other process can be applied
to this invention, although the hydrogen permeable membrane formed
by rolling is used in the embodiment.
First Example
[0030] In a first example, hydrogen permeable membranes (samples
1-1 and 1-2) were subjected to a thermal treatment through the
method in accordance with the embodiment mentioned above. And the
effect was measured. Conditions of the thermal treatment are shown
in Table 2. The sample 1-1 was subjected to the thermal treatment
in a vacuum atmosphere of approximately few tens of Pa. The sample
1-2 was subjected to thermal treatment in a 100% hydrogen
atmosphere. The thermal treatment temperature was set to be 800
degrees centigrade and the thermal treatment time was set to be 5
hours in the case of both of the samples. In the example, a thin
layer composed of palladium was used as the hydrogen permeable
membrane.
TABLE-US-00002 TABLE 2 Thermal treatment Thermal temperature
treatment time Atmosphere Sample 1-1 800 degrees C. 5 hours Vacuum
(few tens of Pa) Sample 1-2 800 degrees C. 5 hours Hydrogen
100%
(Analysis)
[0031] Aspects of the surface of the samples 1-1 and 1-2 after the
thermal treatment are shown in FIG. 2B and FIG. 2C. The hydrogen
permeable membrane before the thermal treatment is referred to a
comparative sample. An aspect of the comparative sample is shown in
FIG. 2A. As shown in FIG. 2A, a polishing scratch was formed on the
surface of the hydrogen permeable membrane before the thermal
treatment. And little grain boundary groove was formed. However, as
shown in FIG. 2B and FIG. 2C, the grain boundary groove was formed
on the hydrogen permeable membrane after the thermal treatment.
Therefore, the metal diffusion in the hydrogen permeable membrane
was facilitated through the thermal treatment. And the surface of
the hydrogen permeable membrane was smoothed compared to the
hydrogen permeable membrane before the thermal treatment. In
particular, the sample 1-2 was smoothed to a large degree. It is
therefore preferable that the hydrogen permeable membrane is
subjected to the thermal treatment in the 100% hydrogen atmosphere
in order to facilitate the metal diffusion.
Second Example
[0032] In a second example, hydrogen permeable membranes (samples
2-1 through 2-3) were subjected to a thermal treatment through the
method in accordance with the embodiment mentioned above. And the
effect was measured. Conditions of the thermal treatment were shown
in Table 3. As shown in Table 3, the thermal treatment temperature
differs with respect to the samples in the example. The thermal
treatment temperature was set to be 600 degrees centigrade with
respect to the sample 2-1. The thermal treatment temperature was
set to be 700 degrees centigrade with respect to the sample 2-2.
The thermal treatment temperature was set to be 800 degrees
centigrade with respect to the sample 2-3. The thermal treatment
time was set to be 5 hours in any cases of the samples. In the
example, a thin layer composed of palladium was used as the
hydrogen permeable membrane.
TABLE-US-00003 TABLE 3 Thermal treatment Thermal temperature
treatment time Atmosphere Sample 2-1 600 degrees C. 5 hours
Hydrogen 100% Sample 2-2 700 degrees C. 5 hours Hydrogen 100%
Sample 2-3 800 degrees C. 5 hours Hydrogen 100%
(Analysis)
[0033] Aspects of the surface of the samples 2-1 through 2-3 after
the thermal treatment are shown in FIG. 3B through FIG. 3D. The
hydrogen permeable membrane before the thermal treatment is
referred to a comparative sample. An aspect of the comparative
sample is shown in FIG. 3A. As shown in FIG. 3B through FIG. 3D,
the surface of each sample was smoothed and the grain boundary
groove was formed after the thermal treatment. The surface was more
smoothed and the grain boundary groove was formed more notably when
the thermal treatment temperature got higher. Therefore, the metal
diffusion in the hydrogen permeable membrane was facilitated by
increasing the thermal treatment temperature. It is therefore
preferable that the thermal treatment temperature is set to be
higher in order to facilitate the metal diffusion.
[0034] FIG. 4A through FIG. 4C illustrate a surface profile of each
sample after the thermal treatment. The vertical axis of each graph
indicates a height of the surface of the samples from a given
reference depth. The horizontal axis of each graph indicates a
position in a width direction of the measured range. As shown in
FIG. 4A, little grain boundary groove was formed on the comparative
sample. An average roughness Ra of the comparative sample was 24
nm. A maximum valley height Rmax of the comparative sample was 100
nm. Here, the average roughness Ra and the maximum valley height
Rmax is a value calculated by a calculation method shown in JIS
B0601.
[0035] On the other hand, the average roughness Ra and the maximum
valley height Rmax of the sample 2-1 were approximately as same as
those of the comparative sample. However, a boundary groove was
formed on the sample 2-1 as shown in FIG. 4B. A boundary groove was
formed notably on the sample 2-3 as shown in FIG. 4C. This is
because the maximum valley height Rmax of the sample 2-3 was a
large value, 137 nm. A grain boundary step was approximately 0.1
.mu.m tall. And the surface of the sample 2-3 was smoothed. This is
because the average roughness Ra of the sample 2-3 was a small
value, 18 nm. In particular, on the sample 2-3, the average
roughness Ra in an area except for the grain boundary groove was
approximately zero. Therefore, it is confirmed that the metal
difusion is facilitated when the thermal treatment temperature is
increased, and that accordingly a grain boundary groove is formed
notably and a surface is smoothed.
[0036] In accordance with the first example and the second example,
the metal diffusion is facilitated when the hydrogen permeable
membrane is subjected to the thermal treatment. The deformation of
the hydrogen permeable membrane is therefore restrained when the
hydrogen permeable membrane is subjected to the thermal treatment
sufficiently. Accordingly, it is possible to restrain the boundary
separation between the hydrogen permeable membrane and the
electrolyte layer caused by the deformation of the hydrogen
permeable membrane, if the hydrogen permeable membrane is subjected
to the thermal treatment sufficiently and the electrolyte layer is
formed on the hydrogen permeable membrane. In addition, it is
confirmed that the atmosphere in the thermal treatment is a vacuum
atmosphere or a 100% hydrogen atmosphere, as a result of the first
example. Further, it is confirmed that the thermal treatment
temperature is preferably set to be higher, as a result of the
second example.
* * * * *